The present invention relates to non-volatile memory fabrication, and more particularly, to a method for resistor-type non-volatile memory fabrication.
Memory devices are typically divided into volatile and non-volatile types. Among non-volatile memory devices, flash memory is the most popular. As semiconductor size is reduced, flash memory devices face challenges of high operating voltage, long operating time, and gate oxide thinning, causing unsatisfactory retention time. Thus, newer non-volatile memory types have been developed to replace flash memories, among which, resistive non-volatile memory provides higher write and erase speeds, low operating voltage, low operating current, long retention time, simple structure, low power consumption, small size, and low cost.
FIG. 1 is a schematic diagram of a conventional resistor-type non-volatile memory 10, disposed on a substrate 12, comprising a dielectric layer 14, a bottom electrode 16, a resistor layer 18, and a top electrode 20. The bottom electrode 16 comprises a platinum film. The resistor layer 18 comprises a chromium (Cr) doped strontium titanate single crystal and provides reversible resistance switching.
FIG. 2 shows a relationship between bias and leakage currents of a conventional non-volatile memory 10. As shown, when the bias voltage applied on the resistive non-volatile memory 10 increases positively from 0 V, the leakage current increases along curve C1. However, when the positive bias exceeds V1, the relationship between the bias and leakage current switches to the curve C2. At that time, leakage current reduces. The relationship follows the curve C2, even if the bias is again reduced. Until a negative bias less than V2 is applied to the resistive non-volatile memory 10, the relationship between the bias and the leakage current switches back to curve C1 along with an increased negatively leakage current, such that resistance of the resistive non-volatile memory 10 is reduced. Because of the special characteristics of resistance switching, the resistive non-volatile memory can be used as a memory. For example, these two different resistances can be used to represent 0 and 1, respectively. When write or erase is required in the memory device, they can easily be implemented by applying proper voltage to the resistive non-volatile memory 10 to change resistance. In addition, data stored therein is retained without requiring power supply.
In conventional fabrication of resistive layer 18, two methods are typically used. In one, a single crystal structure of SrTiO3 is formed with a crystal orientation (100) and then undergoes flame fusion to form a Cr doped SrTiO3 single crystal. Alternatively, a pulse laser sputtering process can be used to grow a Cr doped SrZrO3 film. However, the single crystal structure incurs higher costs, while the latter method is not suitable to form a large area uniform composition film, such that neither method meets requirements of mass production.
Thus, an improved method for non-volatile memory fabrication is called for.